Two of South Africa's Nobel peace prize winners, Archbishop Desmond Tutu and FW de Klerk, have pulled out of a Johannesburg conference to fight racism after what they branded as Pretoria's "disgraceful" decision to ban the Dalai Lama from attending following Chinese pressure.

The Nobel peace prize committee also said it would boycott this Friday's conference, which is dedicated to tackling racism ahead of the 2010 World Cup.

The row threatens to draw in Nelson Mandela, who, with his fellow South African laureates, invited the Tibetan spiritual leader, and further embarrasses South Africa, which has been accused of squandering its moral authority since ending apartheid by blocking UN security council moves to pressure rogue governments in Burma and Zimbabwe.

Tutu, who won the prize for his resistance to white rule, told Johannesburg's Sunday Independent newspaper he will not attend the conference to discuss how to use the World Cup preparations to combat racism and xenophobia if the Tibetan spiritual leader is not present.

"If His Holiness's visa is refused, then I won't take part in the coming 2010 World Cup-related peace conference. I will condemn [the] government's behaviour as disgraceful, in line with our country's abysmal record at the United Nations security council, a total betrayal of our struggle's history," he said.

"We are shamelessly succumbing to Chinese pressure. I feel deeply distressed and ashamed."

The FW de Klerk Foundation, established by South Africa's last white president, said it would also pull out of the conference, albeit reluctantly.

"South Africa is a sovereign constitutional democracy and should not allow other countries to dictate to it regarding who it should and should not admit to its territory," the foundation said in a statement.

"Mr De Klerk has been in touch with Archbishop Tutu and identifies himself with the views that he has expressed with regard to the refusal of the South African government to grant a visa to the Dalai Lama."

The Norwegian Nobel peace prize committee also condemned the South African decision.

"It is impossible for us to be part of an event where one of the main participants is not able to enter the country," said Geir Lundestad, the committee's secretary.

The Tibetan government in exile in India today blamed "intense pressure" from China, which has become one of South Africa's largest trading partners. The claim was apparently confirmed by the Chinese embassy in Pretoria, where the minister counsellor, Dai Bing, was quoted as telling the South African media that his government had warned that allowing the Tibetan spiritual leader to attend the conference would damage bilateral relations.

But the South African government denied its decision had anything to do with Beijing. It said the Dalai Lama had been refused a visa because his presence would draw attention away from the World Cup preparations.

Thabo Masebe, the spokesman for the president, Kgalema Motlanthe, said the conference organisers had not consulted the government before inviting the Tibetan leader.

"We in the South African government have not invited the Dalai Lama to visit South Africa, because it would not be in the interests of South Africa," he said. "The attention of the world is on South Africa because of it being the host country for the 2010 World Cup, and we wouldn't want anything to distract from that."

Pretoria has shied away from the Tibetan leader before. Ten years ago, South Africa's then president, Thabo Mbeki, said he was too busy for a one-to-one meeting with the Dalai Lama.

The actors Morgan Freeman, who is to play Mandela in a new film, and Charlize Theron, a South African, are also due to attend the conference.